Israeli stocks also fell, triggering circuit-breakers to slow declines in the TA-25 Index, which has tumbled 19 percent from a record high in April. The U.S. is a large export market for Israel.

The Middle Eastern exchanges are small and volatile, so it’s not clear if their declines will be mirrored in larger Asian exchanges, which haven’t opened for Monday trading yet. Those are the markets investors will be watching closely in a few hours. Many Asian countries have trade surpluses with the U.S., which they have invested in Treasuries. The downgrade also could cause further erosion of the dollar against Asian currencies.

As the Wall Street Journal points out:

That could give ammunition to Chinese policy makers who have called for China to reallocate some of its reserves, though the dollar’s liquidity and lack of other stable alternatives would limit such moves. China has nearly $3.2 trillion of foreign-exchange reserves, and some estimate that as much as 70% are in dollar-denominated assets.

Trading opens in Sydney at 4 p.m., Houston time, followed by Tokyo at 6 p.m. and Singapore and Hong Kong two hours after that.

Update: Sorry, folks, as some of you have pointed out, I got those times wrong. The Tokyo and Australian exchanges open at 7 p.m., Houston time, Hong Kong opens at 8:30 p.m. and Singapore opens at 8 p.m.